Immunologic reactions are important in determining the clinical outcome of neoplastic disease. Using human prostatic cancers, we will attempt to demonstrate a specific immunologic response and relate it to the stage and extent of disease. Attention will be focused on cell- mediated immunity, since this system has been implicated in tumor control, and on humoral antibodies that interact with cellular factors. We shall explore the nature of the antigens present on the surface of prostatic cancer cells which are involved in these reactions. These studies will provide a rational basis for various kinds of immunologic intervention (immunotherapy) which could modify favorably this disease in man.